FIG. 2.

Features of yeast mRNAs involved in the translation pathway relevant to control. (A) The 5′UTR stretches from the cap to the AUG start codon (positions 1 to 3). (B) Structural features in the 5′UTR that can influence translational efficiency (and mRNA stability) include secondary structures such as stem-loops and poly(G) sequences and short uORFs. uORFs can have a number of important properties, depending on their structure and sequence environment. The main coding region (positions 3 to 5) can sometimes include an in-frame stop codon that either is avoided by frameshifting or, in aberrant mRNAs, leads to premature termination (and mRNA destabilization). The 3′UTR and poly(A) tail (positions 5 to 7) influence the behavior of posttermination ribosomes at the end of the transcript, and at least the poly(A) tail has been implicated in the control of initiation. All of the numbered sites in panel A can be involved in key events of translation or mRNA turnover or act as targets for control mechanisms. The schemes shown are composites of the features of yeast mRNAs that can be involved in posttranscriptional control. Individual mRNAs differ with respect to the combination of the respective sites present. Panel A reproduced from reference 364 with permission of the publisher.